Currently, commercially available silicone hydrogel contact lenses are produced according to a conventional cast molding technique involving use of disposable plastic molds and a mixture of monomers in the presence or absence of macromers. However, disposable plastic molds inherently have unavoidable dimensional variations, because, during injection-molding of plastic molds, fluctuations in the dimensions of molds can occur as a result of fluctuations in the production process (temperatures, pressures, material properties), and also because the resultant molds may undergo non-uniformly shrinking after the injection molding. These dimensional changes in the mold may lead to fluctuations in the parameters of contact lenses to be produced (peak refractive index, diameter, basic curve, central thickness etc.) and to a low fidelity in duplicating complex lens design.
Such disadvantages encountered in a conventional cast-molding technique can be overcome by using the so-called Lightstream Technology™ (CIBA Vision), as illustrated in U.S. Pat. Nos. 5,508,317, 5,789,464, 5,849,810, and 6,800,225, which are incorporated by reference in their entireties. The Lightstream Technology™ involves reusable molds produced in high precision and curing under a spatial limitation of actinic radiation (e.g., UV). Lenses produced according to the Lightstream Technology™ can have high consistency and high fidelity to the original lens design, because of use of reusable, high precision molds. In addition, contact lenses with high quality can be produced at relatively lower cost due to the short curing time and a high production yield.
In order to apply the Lightstream Technology™ in making silicone hydrogel contact lenses, silicone-containing prepolymers have been developed, as described in U.S. Pat. Nos. 6,039,913, 6,043,328, 7,091,283, 7,268,189 and 7,238,750, 7,521,519; commonly-owned US patent application publication Nos. US 2008-0015315 A1, US 2008-0143958 A1, US 2008-0143003 A1, US 2008-0234457 A1, US 2008-0231798 A1, and commonly-owned U.S. patent application Ser. Nos. 12/313,546, 12/616,166 and 12/616,169, which are incorporated by reference in their entireties. However, those types of prepolymers disclosed in the above patents and patent applications may have some practical limitations in their use for making silicone hydrogel contact lenses according to Lightstream Technology™.
A commonly-owned copending U.S. patent application Ser. No. 12/456,364 (herein incorporated by reference in its entirety) discloses a method for making silicone hydrogel contact lenses from a monomer mixture (i.e., a lens-forming composition) according to the Lightstream Technology™. However, it is discovered here that in addition to relatively longer curing time, relatively significant shrinkage during curing of the monomer mixture in molds can occur that may greatly impede the application of the Lightstream Technology™ in the manufacturing of silicone hydrogel contact lenses.
Therefore, there is still a need for new prepolymers suitable for making sislicone hydrogel contact lenses according to the Lightstream Technology™.